This copy is for your personal, non-commercial use only. To order presentation-ready copies for distribution to your colleagues, clients or customers, click the "Reprints" link at the bottom of any article.

“Analysts will be hard pressed to explain how equity markets ended unchanged on the day of an unprecedented policy announcement from the Fed,” El-Erian begins, in a piece for CNBC. “Rather than resort to clichés, they could consider the competing emotions felt by a patient taking an experimental drug that has not been through clinical tests. Let me explain.”

Please.

The "expected and therefore fully priced in" excuse for an unchanged market does not work, he argues.

“A notable component of today's Fed announcement–the shift to quantitative (employment and inflation) thresholds–was a surprise. Most had expected this would not occur until March 2013 at the earliest; and the few outliers had mostly opted for January.”

The second traditional explanation he targets, compensating news, “also does not work. Away from the Fed, it was a relatively quiet day.”

So what’s going on? What accounts for the eerie silence?

El-Erian unleashes the “new drug” argument.

“Professional investors welcomed the news that the Fed is ‘all in’ when it comes to trying new drugs to stimulate the economy,” he writes. “And they fully understand that the transmission mechanism runs right through the equity markets. As [Fed Chairman Ben] Bernanke has stated, the Fed is looking to ‘push investors to take more risks.’ Hence the initial positive reaction to the announcement.

However, later in the day, he notes, and especially when Bernanke answered questions, the enthusiasm dissipated.

The reason was that “as the day proceeded, investors realized that, like any experimental drug, there is a material risk of complications. After all, the Fed's operational modalities are not straightforward; the analytical underpinnings are far from robust; and the Fed's prior experimental measures have not succeeded in generating sustainable growth.”

All this speaks to the aforementioned “competing factors” that were in play on Wednesday. Analysts, El-Erian says, “will have to wait for more definitive evidence on the extent to which investors are willing to romance yet again another experimental and untested measure out of the Fed.”

In the meantime, he concludes, “expect the shift to quantitative thresholds to lead to greater daily volatility, especially around data releases (and most pronounced when the monthly employment reports are released).